The details: Eight months before Election Day, the Secret Service realized that "they were using the wrong formula to calculate the costs" of air travel for the campaigns, per CNN.

Additionally, the agency's policy had been to pay the lower of two options: the lowest available first-class fare or a pro rata share of a campaign charter flight. However, for the latter, it did not require campaigns or charter companies to provide invoices to document the cost of charter flights.

By the numbers: The report shows that an estimated $58 million was spent on air travel related to the campaigns including "two vice presidential candidates and six of the candidates' family members":